According to the OP, the DEALER (not the previous owner) added the Z28 badge, then proceeded to advertise it as a Z28 if you read the exact dealer advertisement.

Doing so as an expectation to increase profit is called copywright infringement. It would NOT be copywright infringement if they had put the Z28 badge on it then proceeded to advertise it as an SS, which is what it is.

Adding the Z28 sticker then ADVERTISING it as a Z28 in writing is where the law is broken.